She began studying Gōjū-ryū Seigokan karate at Ennouji Dojo in junior high school.
She was one of Japan's brightest female martial artists during the 1980s and a leading figure in the girls with guns fad of Hong Kong action cinema.
[citation needed] Oshima portrayed "Farrah Cat" in Bioman, which aired not only in Japan originally but also worldwide.
After her Hong Kong career dried up, she moved to the Philippines in the 1990s and performed under the stage name Cynthia Luster.
She is commonly known to Western audiences as the actress in the Marlboro Lite commercials of the late 1990s.